Frequency response controlling means



Dec. 18, 1951 v GARDNER 2,579,069

FREQUENCY RESPONSE CONTROLLING MEANS Filed June 4, 1948 2 SHEETSSHEET 1 4 4 INVENIOR.

FREDERICK H. GARDNER iz {M ATTO R N EY 1951 F. H. GARDNER 2,579,069

FREQUENCY RESPONSE CONTROLLING MEANS Filed June 4, 1948 2 SHEETS-SHEETZ ROTATION OF f ROTATION OF BASS CONTROL TREBLE CONTROL lOO 1000 I 20000 FREQUENCY'IN CYCLES Fl G 6 INVENTOR.

- FREDERICK H.GARDNER BYJZQM ATTORNEY UNITED STATES: PAT orr ce P mvflwrefi iggg O I iQL IN Frederick H. Gardner,Rochester, N. Y., assignor .to- Stromberg-Carlson Company, a -corporation ofNew York Application June 4, 1948,"S e1 ial No. '31 ,l67

6'Claims.

My invention relates to "frequency response controlling means whereby the frequency re sponse of an audio amplifier may be adjustably controlled-or-varied.

In order to permit the user'of an amplifier to adjust'the frequency response of the sound-re-' produced by the amplifier according to 'his'individual preferences or to accommodate peculiar local conditions, it is desirable to provide tone control means. Accordingly,'-it is an object of my invention to provide new and improved-tone com trol means according towhich both treble and portions of the reproduced sound may be controlled.

' Other objects and advantages-of my invention will become apparent as "the followin description proceeds, andthe features of novelty which characterize my invention will be pointed out with particularity inthe claims annexed to and forming a part of this specification. For a better understanding of my invention, reference may be hadto the accompanying drawing inw-hich Figs. 1 and '2 illustrate d-ifierentembodiments of my invention utilizing frequency control oi the relativelyhigh frequency components of thesig nalsbeing reproduced; Fig. 3 illustrates 'an' ern bodiment "of my invention according to--- which the lower-frequencies are controlled; Figs. 4 an'd 5 'illustr'ate amplifiers provided with both bass and treble control; and Fig. 6 a; family-of curves useful in understandingfthe principlesof my invention.

"In accordance with my invention, I contemmate; the application 'ofbass or tieb'le} or-- both, controlstoat'le'ast one'stageof an-audio amplifier. My invention may precede the first'sta'ge or be inserted betweenstag'es or acom'bination of locations may be employed. The invention c'om-f rises in one embodiment, forexample an'electron discharge device having input and output circuits. The treble control includes resistance in one side of the input circuit-and'a capacitance across the input circuit, one side ofthe capacitance being preferably adjustably connected to the resistance. The base control-comprises a variable resistance shunting the-inputcir'cuit of one of the stages of the amplifier and a capacitor connected in one side of the input clrcuit on the input side of the variable resistance. Referring-to the drawing,-Fig. 1 shows iii-schematic form a portion of anamplifier-providedwith tone control means which makes possible the-variation of the high-frequency response by varying .the high'frequency cutofi point for the network." T-wo stages'of control are shown in order to illustrate the application of twostages, although only one stage 'or more than two stages maybe usedif desired.

The. firstzstage.-' lustratedj in Fig; 1 comprises V 2. an electron discharge. device 1 ofsuitable' -type, illustrated in l the :iarawmgyas being one of the pentode type. 1 The an'ode 2- is 'conne'cted to a suitable sou' rce of positive-potential as thro h" a suitablere'sistor 3 and to the next sta'ge o f the" amplifier through a su-i'table coupling capacitor 4. The discharge --device lisbiasedin 'somesuitable manner. in" the illustratedembodiment of my invention; there is provided-a s'uitable source of direct current potential. 5 connected betweeri'the cathode 6 ahdg round. The input or grid-circuit is-cor'np'leted through asuitable resistor T con-- n'ect'ed between ground and control" electrode or grid'8'ofdevice I.

"Means is provided to vary' the point of high frequency cut-off. In Fig. lg this=means comprisics a suitable tone control lr which may include a potentiometer 113- connected: between a sui-table' source ofinput -signa-l as indic'ated Jay the ten-- ml-nals 1 H and -the-control electrode Biand asuitable capacitor lz connected betweenithe :arm of the potentiometer .rmm a point of =predeter mined potential; such ascgrouhd. Thereiis ial'so. represented in series with the potentiometera llla' resistor Rs. :RS' represents the gresistance .iof; the sourcesof the' inputisignal, 1. e., themesistarfce 1of.l the system-precedin the :tone .control resistance. or potentiometeretll.

Thesecondstage ofitonecontrol is, .athe same iasv that illustrated in .the firstsstage as willabesa-p. parent' from a comparison :oimhe. left and right handportion'sof l ig. '1. 'It willsbe iunderstoodthat' thfiipl'infiiplBSfif myinvention are not limited to the use of apoten-. tiometeru .Ffor1;example,:;inFig; 2, there dspilldstrated a modification of .the arrangement: ofJFig, 1,. in which a conventional: variable wesistor tlllazisc substituted ront-he; potentiometer U1. .Thencone trol electrode. 8 :in this embodiment. of.my invene tion is 1 connected 2170' 1 the yariable point. of the resistor,-as;.byiconnectionvto.a tap .or;to..a;m0s?ah1e. arm; iias shown; instead. of to ithej .rightliand, end of potentiometer-IIitiof' liig. 1. In Fig. ,2. com-i ponentsf:identicali/to. those illustrated-in Eig; '1. arev representedzby .the same. 'numeralszas :usedzin Fig. 1. 'In Orderxtodescribe :the theory of operatj n zpf the treble itoneicontrol;disclosedfherein, it is s-- s'umed that-Rs; is the: resistance10f. the son e input, R0 :isithezload; on ,thestone contliolnetworlgi. e, h input-resistance, of d s har "del qel R1 is: the 7 amount of resistance ofotentiometer. l 0:. on, the :input side of; the arm; of potentiometer; [0, R2 is the amount of-resistanceon; the .outp ut side of -thearm ofpotentiometer L0, Cisth capacity oi capacitor l 2, andX is thecapacitive 3- aetance of: capacitor 13. ,In this connection reference is made to the-curves of ,Fig. 6. T The, ht

of. I

settings of potentiometer ID on the output level expressed in decibels vs. frequency. Curve A represents the condition when the arms of potentiometer I is at the extreme left as viewed in Fig. 1, i. e., R1 is equal to zero, curve D represents a condition in which the potentiometer arm is at the extreme right as viewed in Fig. 1, i. e., R1 is maximum and R2 is equal to zero, and curve B and C represent intermediate positions of the potentiometer.

Inspection of Fig. 1 indicatesthat Rs, potentiometer III and capacitor I2 constitute a voltage divider. Then, if R0 is much greater than Rs and if R5 is small with respect to the reactance of capacitor I2 for the highest frequency to be passed (a condition which is met when the capacity of the capacitor I2 is small), and R1 is equal to zero, most of the signal voltage appears across capacitor I2. If cutoff be considered that level at, which attenuation attains 3 db, the pass band of the circuit shown in Fig. 1 under the conditionsassumed (curve A of Fig. 6) is approximately 50 cycles to something in excess of 20,000 cycles. The high frequency cutoff point (where the output voltage E0 is reduced to a value 3 db below full output) is the point where Xe is equal to the sum of R5 and R1. Since G and Rs are fixed, the high cutofi point may be controlled by adjusting potentiometer ID to vary R1 whereby the range of control depends on the total resistance of the potentiometer (R and R2) and the capacitance of capacitor I2.

If potentiometer I0 is moved to the other extreme, R1 becomes maximum andRz becomes zero in which case the resistance on the input side of the arm of the potentiometer increases by an amount R1 and hence less voltage drop exists across capacitor I2. Referring to Fig. 6, the cutoff level is now reached at approximately 1100 cycles.

When a plurality of stages of control are used, the plate resistance of all electron discharge devices except the last and the anode resistors associated therewith should be of relatively low resistance compared to R1 and R2 and the control electrode or grid resistors should be of relatively high value with respect. to thesum of R1 and R2 in order to provide a relatively high impedance and relatively little voltage dropacross potentiometer I0. Y 7

By providing a plurality of stages as shown in Figs. 1 and 2, there results sharper attenuation characteristics and there is illustrated treble control on the input side of a stage as well as treble.

control between two stages of an audio amplifier.

In some cases, it may be desirable toinclude a suitable capacitor I8 in shunt with the right hand portion of potentiometer. I 0, as indicated in dotted lines in Fig. l, as, for example, when tubes of the triode type are used, or where. it is desired to compensate for any high frequency losses resulting from the use of shielded leads.

Referring to Fig. 3, there is illustrated two stages of amplification embodying bass control or' means for varying the low frequency cut-off of the amplifier. The arrangement disclosed in Fig. 3 comprises a suitable electron discharge device I3 illustrated as of the pentode type connected to a suitable source of input signal II through a suitable capacitor I4 and resistance R; representing the resistance of the source. Be-- tween the control electrode I5 of electron discharge device I3 and ground, there is connected a suitable variable resistance I6 and a fixed re-' sistance I'I, although if preferred, a single-posistance I6 is equal to zero.

capacitive reactance of the coupling capacitor I4v 4 tentiometer or resistor, variable in nature, may be provided. With this arrangement, capacitor I4 is on the input side of resistances I6 and I I and the arm of the potentiometer or resistance I6 is connected to ground so that the lower portion, as viewed in Fig. 3, is shortcircuited. With this arrangement, capacitor I4 and resistors I6 and I1 constitute a resistance-capacitance network. Again, cutofi may be considered to be the frequency where attenuation reaches a loss of 3 db. Under this condition, if Rs is much less than the value of resistance of resistor H, the low frequency cut-off point is that frequency where the capacitive reactance of capacitor I4 isequal to the sum of resistances I6 and [1.

Referring to Fig. 6, the left hand portion of the figure illustrates various conditions for different settings of the bass control of resistor l6. Assuming that the treble control illustrated in Figs. 1 and 2 is in the position for curve A, curve G is then representative of the condition wherein re- At this point, the

is equal to the resistance of resistor I1 and the low frequency cut-oil point is approximately 250 cycles. If the setting of potentiometer I6 is varied so that all of its resistance is inserted in,

circuit, the response is indicated by curve A in Fig. 6 and the cut-01f frequency becomes approxi{ mately cycles. Figs. 6E and SF represent intermediate settings of control I6 with cut-off fre-' Fig. 4 shows a single stage amplifier embody ing both bass and treble controls of the type shown in Figs. 1 and 3, respectively. There is illustrated an electron discharge device 53. 'Input signals are applied to the control electrode 54 of device 53 through a suitable first capacitor resistance 56.

terminals 20 and 2I which may, for example, be

suitably arranged for microphone and phono graph, respectively. Input terminal 20 is shown connected to the control electrode of a suitable electron discharge device 22 which may be one half of a type 6SC7 tube. The output of electron discharge device 22 is impressed across the bass controlsection 23 including a suitable capacitor 24 and. resistances 26 and 21, and the anode of device 22 is also connected to a suitable source of direct current through a suitable anode resistor 25.

The output of the bass control section may be connected through a suitable capacitor 28 shunted by a suitable resistor 29 to compensate for any high frequency losses in other parts of the amplifier -to the control electrode of an electrondischarge device ;30 which may be one half of a type 6807 tube, although in most cases capacitor 28 and resistor 29 may be omitted. The anode discharge device 30 is connected to a suitable, source of positive potential through a suitable,

anode resistor (II and to the control electrode of, the next stage 32 of the amplifier, whichmay be one has ef -a type enfz; tubef thciig tietie controlsection aajccmprismg spot ete 34 cd nected in series with the anode of discharge device-'30 and device 32, arid eapseiter 3-5 *is connected between the arm ofpotentiomter 34 and ground. Capacitor 3B is connected'between the arm of potentiometer and the output "end ofthe resistance portion of potentidmeter'M; The output'ofdischarge device 32 is connected to a suitable output transformer 43. Feedback, if desired, may be provided asby means of series connected capacitor 3! and resistor 38 connected between anode and control electrode of device .32. The output side of treble cont'r'ol33 is also connected to the control electrode of asuitable discharge device 39 which maybe, the other half of the second-mentioned type {GSC'Y tube througha suitable coupling resistor 40. {The controiflectrode of device 391s also connected tq'ground through a suitable resistor H. The anode of device 39 is connected to a suitable source of positive potential through anode resistor 44 and to the control electrode of asuitable discharge. device 42 which may be the other half of th'etype 6N7 tube. The anode of discharge device 42 is connected to the output, transformer 43.

The second pair of input terminals 2! is shown connected to the control electrode of discharge device 45 which may be the other half of the first-mentioned type 6807 tube. The output of device 45 is impressed across treble control section 4'! through a suitable coupling capacitor 46. The treble control section 4'! comprises a potentiometer 48 and a capacitor 49 connected between the arm of the potentiometer and ground. Inasmuch as a tube of the triode type is employed, capacitor 50 is connected between the arm of the potentiometer 48 and the right hand end of potentiometer 48 as viewed in Fig. 5. The output side of treble section 41 is connected to the control electrode of discharge device 30 through a suitable coupling resistor 5|. The control electrode of device 30 is also connected to ground through a suitable resistor 52. Treble sections 33 and 41 may be arranged for simultaneous adjustment as indicated by the dashed lines in Fig. 5.

Typical values for the various components of the amplifier illustrated in Fig. 5 are as follows:

Devices 22 and 45, type 6SC7 tube Devices 30 and 39, type 6S0? tube Devices 32 and 42, type 6N7 tube Resistor 25, 22,000 ohms Resistor 28, 47,000 ohms Resistor 21, 5 megohms Resistor 29, .47 megohm Resistor 3|, 22,000 ohms Resistor 34, .25 megohm Resistor 38, 4.7 megohms Resistor 40, .33 megohm Resistor 4!, 10,000 ohms Resistor 44, 47,000 ohms Resistor 48, .25 megohm Resistor 5|, .15 megohm Resistor 52, .22 megohm Capacitor 24, .01 microfarad Capacitor 28, 50 micro microfarads Capacitor 35, 1000 micro microfarads Capacitor 36, 150 micro microfarads Capacitor 31, .1 microfarad Capacitor 46, .1 microfarad Capacitor 49, 470 micro microfarads Capacitor 50, 150 micro microfarads vvhrie shave shown and sexiness-particular einbbdiment of 'myin'vention, it will be obvio'ii's to those skilled in the art that changes and'hio'di fications may be made without departing from my invention in its broader aspects. For enampl, *iny invention is also applicable topush-pull amplifiers. I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scopeof myinvention. 3

'Iclaim: a r

1. In -an audio amplifier, an electron discharge device having input and output circuits, means for impressing signals to be amplified on said input circuit, means for varying the high free, quency cut-off point of said signals comprising-a potentiometer connected in seriesin one side of- Saidiinput circuit and a first capacitor connected between the arm of said potentiometer and theother side of said input circuit, and means' for varying the low frequency cut-off point of s'aid signals comprising a second capacitor connected on the input side of said potentiometer and'a variable resistance connected from a point he: tween-said'second capacitor and said potentiometer and the other side of said input circuit.

2. In an audio amplifier, an electron discharge device having input and output circuits, means for impressing signals to be amplified on said input circuit, means for varying the high frequency cut-off point of said signals comprising a. potentiometer connected in series in one side of said input circuit and a first capacitor connected between the arm of said potentiometer and the other side of said input circuit, means for varying the low frequency cut-0n point of said signals comprising a second capacitor connected in series with said potentiometer on the input side thereof and a variable resistance connected from a point between said second capacitor and said potentiometer and the other side of said input circuit, and a, third capacitor connected between the arm of said potentiometer and the output side of said potentiometer.

3. In an audio amplifier, an electron discharge device having an anode, a cathode, and a, control electrode; an output circuit between said anode and said cathode; an input circuit between said control electrode and said cathode; means for impressing signals to be reproduced on said input circuit; a second electron discharge device having an anode, a cathode, and a control electrode; means for impressing signals appearing in the output circuit of said first electron discharge device upon the control electrode of said second electron discharge device; means'including a first capacitor and a resistance connected in series with the control electrode of said second electron discharge device, said first capacitor being connected on the input side of said series resistance, and a. second capacitor adjustably connected to a point of said resistance and a point of predetermined potential, whereby the high frequency cutoff is adjustable; and a variable resistance connected from a point between said first capacitor and said series resistance to said point of predetermined potential whereby the low frequency cut-off is adjustable.

4. In an audio amplifier, an electron discharge device having an input circuit and treble tone control means in said input circuit comprising a single series connected resistance in one side of said input circuit and a' shunt connected capacitor, one terminal of said capacitor being adjustably connected to said resistance, and the other terminal of said capacitor being directly connected to the other side of said input circuit, whereby the high frequency cutoiT point of said amplifier is adjustable.

5. In an audio amplifier, a pair of electron discharge devices, each having an anode, a cathode, and a control electrode, one of said devices having an output circuit connected'between its anode and cathode thereof, the other of said discharge device having an input circuit connected between its control electrode and: its cathode, means for varying the high frequency cutoff of signals being passed through said amplifier for reproduction comprising a capacitor connected to the anode of the first electron discharge device and a single series connected resistor connected between said capacitor and the control electrode of the second electron discharge device, and a second capacitor adjustably and directly connected between a point on said resistor and said cathode. V

6. In an audio amplifier, an electron discharge device having an input circuit and treble tone control means in said input circuit comprising a single series connected resistance in one side of iii 8, said input circuit and a shunt connected-cacao; tor, one terminal of said shunt connected capacitor being adjustably connected to said resistance, the other terminal of said shunt connected capacitor being directly connected to the other side of said input circuit whereby the high frequency cut-off point of said amplifier is adjustable, and another capacitor connected between said one terminal and the output side of said resistance.

FREDERICK GARDNER.

REFERENCES CITED Thev following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name v Date 4 1,862,458 Barstow June 7, 1932 1,914,629 Aguirre June 20, 1933 2,037,285 Tasker Apr. 14, 1936 FOREIGN PATENTS Number Country Date 152,127 Austria Dec. 27, 1937 

